Implantable medical devices, such as electrical stimulators or fluid delivery pumps, may be used to deliver therapy to patients to alleviate any of a variety of symptoms or conditions. Electrical stimulators, for example, may be used to deliver electrical stimulation therapy to patients to treat a variety of symptoms or conditions such as chronic pain, tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, or gastroparesis. In general, an implantable stimulator may deliver stimulation therapy (e.g., neurostimulation therapy) in the form of electrical pulses or continuous waveforms. An implantable stimulator may deliver stimulation therapy via one or more leads that include electrodes located proximate to target locations associated with the brain, the spinal cord, pelvic nerves, peripheral nerves, or the gastrointestinal tract of a patient. Hence, stimulation may be used in different therapeutic applications, such as deep brain stimulation (DBS), spinal cord stimulation (SCS), pelvic stimulation, gastric stimulation, or peripheral nerve stimulation. Stimulation also may be used for muscle stimulation, e.g., functional electrical stimulation (FES), to promote muscle movement or prevent atrophy.